Telephone set



J. W. FOLEY TELEPHONE SET Dec. 11, 1934.

'Filed June 25, 1932 2 Sheets-Sheet 1 lNVE/VTOR By J. n. FOLEY Dec. 11,1934.

FIG!

J. W. FOLEY TELEPHONE SET Filed June 23, 1932 2 Sheets-Sheet 2 INVENTORJ. M. FOL EV A TTORNEY Patented Dec. 11,

UNlTE fiTATES nsists PATENT orrics Application June 23, 1932, Serial No.618,813

4 Claims.

This invention relates to telephone sets and more particularly toportable telephone sets of the type used by members of a train crew incommunicating from various parts of the system with a central station. 7I

In using a portable telephone set the user is sometimes subjected torather severe electrical shocks by reason of the connecting of the setto lines carrying comparatively highv potentials or lines in whichcomparatively high voltages have been induced from nearby high potentiallines. These high potentials also have a. tendency to cause disruptionof parts of the telephone apparatus in the portable set. v

The object of this invention, therefore, is to protect the user of theset and various pieces of apparatus in the set from injurious effectsfrom high potentials on a line.

In the present invention the telephone set has no direct conncction'witha bridge circuit'con nected to line wires but merely an inductiveconnection therewith through the induction coil. The switch is entirelyin the local circuit in the telephone set and has no direct connectionwith the bridge circuit. Operation of the switch changes the effectivelength of only one of the windings of the induction coil provides meansfor obtaining a step-up transformer eifect in the inductive couplingbetween the telephone set and the bridge circuit when the set is beingused for transmitting.

In the drawings:

Fig. 1 is a schematic of the portable telephone set of this inventionconnected to a pair of open wire lines which lead to a central stationnot shown, and y Fig. 2 is a view in perspective and partly in sectionof the telephone handset used in the invention.

In Fig. 1 in the drawings, 1 and 2 are open wire lines extending, forinstance, along the railway system. To these open-wire lines a portableset 3 may be connected by means of the leads 4 and 5. The portable setcomprises a generator 6, induction coil 7, a telephone instrument 8 andlocal battery 9. When the portable telephone set 3 is connected to theline wires 1 and 2 by means of the conductors 4 and 5, as shown in thedrawings, the following circuit is established: Line wire 1, conductor4, conductor l, normal contacts 10 and 11 of the generator 6, conductor12, condenser 13, right-hand winding of the induction coil 7, conductor14, conductor 5 to line wire 2. It will be seen, therefore, that thetelephone instrument 8 per se which has been shown in the drawings as ahandset telephone comprising the transmitter 15, receiver 16, and aswitch 17,1ocated in the handset, as shown for example in K. WemanPatent 843,653, issued Feb. 5, 1907, is not in any way directlyconnected to line wires 1 and 2 but is only inductively associatedtherewith through the induction coil'l. The local circuit of thetelephone set 8 per se for listeningis iollo 's: Left-hand winding ofthe induction coil, 7, conductor 18, conductor 19, receiver 16,,conductor 20, inner right-hand spring contact 21 of switch 17, outerright-hand spring contact 22 to the lefthand winding of induction coil7. When the switch 17 is in the listening position as shown in Fig. 1 ofthe drawings, with the right-hand spring contacts 21 and 22 closed, theventire left-hand winding of the induction coil '7 is in condition forinductively receiving voice currents from the right-hand Winding.

When the transmitter is to be used, the switch 17 is operated to movethe inner right-hand springcontact 21 away from contact 22, against theinner left-hand contact 23 and to close the inner left-hand contact 23against the outer left-hand contact 24. The left-hand winding of theinduction coil 7 is tapped in the center by conductor 25 which is led tothe inner left-hand spring contact 23 of switch'l'l so that by operatingthe switch 17 to open the contacts 21 and 22 and close the contacts 21,23 and 24 half of the left-hand winding of the induction coil 7 isretained in the circuit of the telephone instrument 8 per se and theother half is disconnected therefrom. When the switch 17 is operated toopen the normally closed spring contacts 21 and 22 and close thenormally open contacts 21, 23 and 24, the following transmitter circuitfor the telephone set 8 per se is obtained; Negative terminal of localbattery 9, conductor 18, lower half of the left-hand winding of theinduction coil 7, conductor 25, closed left-hand spring contacts 23 and24 of switch 17, conductor 27, transmitter 15 to the positive terminalof local battery 9. A listening circuit is also maintained for thereceiver 16 as follows: Lower half of the lefthand winding of inductioncoil 7, conductor 25, inner left-hand spring contact 23 of switch 17,inner right-hand spring contact 21, conductor 20, receiver 16, conductor19, conductor 18, to the other end of the lower left-hand portion of theinduction coil 7.

t is obvious from the foregoing description and by reference to thedrawings that with the switch 17 operated to transmitting position thelower half of the left-hand winding of the induction coil 7 is the onlyportion of the left-hand winding in circuit connection with thetransmitter; that the entire right-hand winding of the induction coil 7is employed as a secondary and that a step-up transformer effect isobtained in the induction coil 7 for transmitting. By operating switch17 to the position for transmitting and thereby reducing the efiectivelength of the left-hand winding of the induction coil 7 a stepdowntransformer efiect is obtained in the induction coil 7 for the receiver16 and sidetone is reduced in the receiver.

The switch 17 being entirely in the local circuit of the telephone set 8per se and having no direct connection through any of its contacts withthe bridge circuit which is connected by way of the conductors 4 and 5to the line wires 1 and 2, respectively, does not provide a path throughits comparatively closely associated contacts for any high potentials inthe line wires 1 and 2.

The generator 6 is located in the bridge circuit and impresses ringingcurrent from the portable set over the line wires 1 and 2 to the centralstation. When the generator handle 28 is turned, spring contact 10 isseparated from contact 11 and brought into engagement with contact 29.Ringing current developed in the coil 30 of the generator 6, thereuponflows by way of conductors 4' and 4 and 14 and 5 over the respectiveline wires 1 and 2.

Separation of the switch and the telephone set per se from the bridgecircuit in the manner above described permits the use of a standard lowpotential telephone instrument and switch 17, the locating of the switchwithin the handle of the telephone instrument 8, as shown in Fig. 2, andthe employment of standard low potential telephone cords.

What is claimed is:

1. A telephone set comprising a bridge circuit to be directly connectedto line wires, a handset including transmitter and receiver elements, alocal battery, an induction coil inductively connecting said handset tosaid bridge circuit, and a switch in the handset for changing theeffective length of one of the windings of the induction coil, thecontacts of said switch being entirely within the circuit of thehandset.

2. A telephone set comprising a bridge circuit to be connected to linewires, a handset including transmitter and receiver elements, a localbattery, an induction coil forming an inductive connection between saidbridge circuit and said handset, and a switch in the handset to changethe eifective length of one of the windings of the induction coil, thecontacts of said switch being entirely within the circuit of the handsetand the switch operating to change the efiective length of the windingof the induction coil on the handset side of the set to obtain a step-uptransformer effect in the induction coil for transmitting.

3. A telephone set comprising a bridge circuit to be connected to linewires, a handset including transmitter and receiver elements, aninduction coil forming an inductive connection between said bridgecircuit and said handset, a local battery, and a switch, said switch andits contacts being entirely within the handset, said switch having anintermediate connection with the winding of the induction coil on thehandset side of the set and operating to change the transformer ratiobetween the windings of the induction coil from an efiicient ratio forreceiving to a ratio more eflicient for transmitting.

4. In combination, a pair of line wires, a bridge circuit adapted to beconnected across said line wires, a handset, an induction coilinductively connecting said handset to said bridge circuit, a localbattery in circuit with said handset, and a switch in the handset forchanging the transformer ratio of the induction coil solely by changingthe effective length of one of the windings of the induction coil, thecontacts of said switch being entirely within the circuit of thehandset.

JOHN W. FOLEY.

